There are so-called two-piece automotive wheels in which a generally cylindrical wheel rim and a generally disc-like wheel disc are welded to each other. As such two-piece automotive wheels, there are known full-face automotive wheels in which a front flange portion is formed at an outer peripheral edge portion of the wheel disc.
An example of the full-face automotive wheels is proposed in No. JP-A-Hei 11-042901 (“JP '901”), for example. As shown in FIG. 8, a wheel rim “f” includes a front bead seat portion “g” provided at one opening edge portion and a back flange portion “j” provided at the other opening edge portion. A wheel disc “p” includes a front flange portion “r” provided at an outer peripheral edge portion and folded backward in a curved shape. An opening end portion “h” of the front bead seat portion “g” of the wheel rim “f” and an inner peripheral end portion “v” of the front flange portion “r” of the wheel disc “p” are welded to each other over the entire circumference of the wheel to form a full-face automotive wheel “m”. The thus configured full-face automotive wheel “m” can secure a large design surface on the wheel disc “p”, advantageously providing high design quality.
In the configuration disclosed in JP '901 described above, the opening end portion “h” of the front bead seat portion “g” of the wheel rim “f” and the inner peripheral end portion “v” of the front flange portion “r” of the wheel disc “p” are welded to each other so that a welded portion “i” joins the wheel rim “f” and the wheel disc “p” to each other. When an automobile equipped with the automotive wheel “m” is running, a load acts on the wheel rim “f” via a tire, and a load acts on the wheel disc “p” via an axle. The front flange portion “r” of the automotive wheel “m” is folded backward in a curved shape and has a generally U-shaped cross-section. Due to the shape of the front flange portion “r” described above, the front flange portion “r” tends to be repeatedly elastically deformed by the load acting on the wheel rim “f” and the load acting on the wheel disc “p”, and tends to be subjected to a stress concentration. Further, because the front flange portion “r” is folded backward through a pressing process or the like, a residual stress may be caused at a curved outermost peripheral edge portion of the front flange portion “r”. The durability of the front flange portion “r” is limited by the residual stress and the stress concentration due to the loads described above.
In addition, a proposal is made for forming a plurality of drain holes “k” through the front flange portion “r” described above in the configuration disclosed JP '901. The drain holes “k” are provided in order to drain rainwater and so on accumulated in the inner space of the front flange portion “r” because rainwater and so on tend to be accumulated therein while the automobile is running. When the drain holes “k” are provided as described above, there is a possibility that the durability limit of the front flange portion “r” is further reduced when the front flange portion “r” is repeatedly deformed.